Idle surge

Brand new to tuning and recently went from a 102Tb to a 103 and now have a idle surge about 300-400 rpm while car is in gear. Drives just fine but surges while sitting at stop light.

Has anyone else had a similar problem or have advice on how to fix?

Hi Christopher,

Has the ECU been remapped to accommodate the change in size of the throttle body? 102mm to 103mm is around 2.5% more area for the throttle plate, this can make a big difference to the amount of airflow past the blade at low throttle openings and this may not be correctly being compensated for.

No it hasn’t been remapped to accommodate for the 103.

I’m new to tuning and still learning and having trouble figuring out what I need to change to fix the surge

A lot of the throttle bodies in that size range also don't have much precision of control especially when near closed, so I would compare your logs from before and after the swap and see if the throttle plate position is getting stuck then jumping, or perhaps moving in larger steps on the new one as well. You may be running into a combination of the calibration having room for optimization and physical limitations.